added at the year's end. The Egyptians' failure to account for the extra fraction of a day, however, caused their calendar to drift gradually into error.

Examples

The oldest solar calendars include the Julian calendar and the Coptic calendar. They both have a year of 365 days, which is extended to 366 once every four years, without exception, so have a mean year of 365.25 days. As solar calendars became more accurate, they evolved into two types.

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